Tek3, XTX200, and XTX50. MTX-RC has not passed to my knowledge
They have different sets depending on the teams down there and some level of individual diver preference from my students that were working there. They preferred the double hoses and Poseidons to the Sherwood and Mares.
Key word "used", also the objection to Atomic and Scubapro is that while an experienced diver can dive damned near any regulator under the ice without issue provided there is no major incident that elevates the SAC rates it does not make them the best choice to go under the ice. Sherwood dry bleeds are a great system, the SPEC boots and similar are not.
You have to have a pretty strong inhale to keep it from chattering, doesn't have rails to deal with lights, doesn't have a weight system to my knowledge *though I haven't had any real issue from it being "floaty"* and it will take the OTS comms for the AGA but they go in upside-down compared to the AGA and the cables come out the wrong side which is weird. I love mine for personal use when I need comms, but I do keep an AGA around just in case I'm in with a big team and need something a bit less unique.
Oh interesting, that's a very different take than when talked to the DSO from down there.